1. Field of the Invention
The present invention generally relates to test methods and devices and more particularly to improved bacterial isolation test methods and devices.
2. Description of the Prior Art
Certain conventional methods for isolating bacteria from body excretions, fluids, tissues, etc. in the detection of diseases usually include the addition to the nutritive culture medium of carefully selected amounts and types of bactericidal, bacteriostatic or similar agents which eliminate or inhibit the development of unwanted or interfering bacteria from the test field, particularly when swarming bacteria, such as various proteus species, may be present, as in cervical or rectal cultures. Swarming bacteria have the ability to migrate and overgrow and thus obscure non-migrating types of bacteria. When isolation grids are used to divide the culture into a series of isolated areas, the swarming bacteria in one or more such areas still can readily migrate through the nutritive medium and under the grid, even if only a microscopic gap exists between the grid and the test container in which the grid is disposed. The bacteria then overgrow other bacteria in other isolated grid areas, thus rendering the test useless. The correct selection and use of bactericical or bacteriostatic agents, etc. requires skill and may result in the elimination or inhibition of other bacteria which are possibly pathogenic and therefore important to the diagnosis and which otherwise might have been detected in the test. Accordingly, it has been a frequent practice of running a second bacterial isolation test under usually modified conditions, e.g. by changing or eliminating the bactericidal and bacteriostatic agents, not only to confirm the first test's results, but to increase the likelihood of detecting other pathogenic bacteria masked by putting in such agents. Such double test procedures are expensive and time consuming, utilizing expensive chemicals, antibiotics and the like, and are subject to a certain degree of error. Accordingly, there has been a need for a simple, inexpensive, rapid and more effective bacterial isolation method and device for detecting bacteria in a culture in which swarming interfering bacteria may be present.
Attempts have been made as shown in the prior art to provide simultaneous multiple tests in a single container having a common culture supporting medium. The Farmer U.S. Pat. No. 3,715,280 discloses such an arrangement which uses a cellular divider inserted into a container having a homogeneous culture supporting medium therein. The respective walls of the container and the divider are said to be configured to fit closely together. However this fails to guarantee the desired isolation between cells, particularly where swarming bacteria are to be cultured, since minute gaps providing inter-cell bacteria growth channels are inevitable. Moreover, such an arrangement requires especially configured dividers and container to try to achieve isolation and cannot make use of the commonly available, low-cost Petri dishes which generally have somewhat irregular and uneven interior wall and bottom surfaces.
Special multi-cell structures for achieving the desired isolation between individual cells are disclosed in Brown et al. U.S. Pat. No. 3,107,204 and Fink U.S. Pat. No. 3,632,478, for example. These structures incorporate the dividers integrally with the container so that the container comprises a plurality of separate sections. While these may be effective for the purpose intended, they appear to be considerably more expensive to fabricate than the patented structure described above and would not work when swarming bacteria are involved, since in streaking these cells one cannot insure there are no swarming bacteria in the cells.
Still another proposed solution to the problem of providing isolation between multiple test cells is disclosed in Saxholm U.S. Pat. No. 3,791,930. However, as with the others, effective isolation depends on establishing sealing contact between the cell walls and the bottom of the container. Any minute gap voids the desired isolation and renders the device ineffective, at least for use with swarming bacteria cultures.